1. A section mixing method refers to the method of preparing mixed rubber after completing the addition of all compounds at one time, and is often used to prepare those rubber materials with good scorching performance and no or only a small amount of active compounds. In order to ensure that the temperature of the rubber in the mixing does not rise too fast, a period of low-speed mixing is generally carried out in the mixer. The method is to add compounding agents (including fillers, operating oils, vulcanizing agents, accelerators, etc.) to the plastic raw rubber in turn. The mixing cycle depends on the characteristics of the compound and the rotor speed. In a period of mixing, the vulcanizing agent and accelerator are generally added within about 60s before the end of the mixer, or the vulcanizing agent and accelerator are added to the mill in the lower piece after discharging. However, no matter which method is used to add vulcanizing agent and accelerator, the temperature of the compound during operation must be controlled below 110 degrees (sulfur and accelerator system) or 120 degrees (DCP vulcanization system) to prevent scorching of the rubber material, and it must be adjusted according to different vulcanization systems. Compounding agents that are not easy to disperse or compounding agents with small dosages can usually be prepared into various masterbatch granules or paste-like mixtures to facilitate addition and rapid mixing into the glue.

A section of mixing method must strictly abide by the requirements of the process conditions such as the addition order of the compound, the mixing temperature, and the mixing time, and the pressure of the upper top plug and the position of the upper top plug in the mixing process should also be paid attention to. Compared with the two-stage or multi-stage mixing method, the tableting, cooling and stopping time between each stage is saved, the production efficiency is improved, and the manufacturing cost of the compound is reduced. However, the premise is that the performance of the mixer (mainly cooling capacity, speed regulation ability and temperature control ability) is required, and there must be enough mixing time to achieve the required degree of dispersion.

The disadvantages of the one-stage mixing method are: the plasticity of the prepared compound is low (Mooney viscosity is higher), carbon black and other compounding agents are sometimes not easy to disperse uniformly, easy to produce scorching danger, and the physical and mechanical properties of vulcanized rubber are relatively low.

The one-stage mixing method is only suitable for general purpose (relatively slow vulcanization) compounding and should be used with caution in large mixers and with caution in the preparation of high-filling, high-viscosity or high-hardness compounds. As an improvement, the rubber discharged from the mixer can be sufficiently cooled on the next sheet mill before adding vulcanizing agents and accelerators.

2. The two-stage mixing method is basically the same as the one-stage mixing method, but it does not contain vulcanizing agents and active accelerators. First make a section of mixed rubber (usually called master compound), and then cool and park for a period of time (generally more than 16h). In order to better disperse carbon black in rubber and improve production efficiency, a fast (more than 40r/min) mixer is usually used to prepare a section of masterbatch, and sometimes the preparation process of masterbatch rubber is combined with the plasticizing process. The subsequent two-stage mixing is based on the first stage of mixing, and then adding vulcanizers, accelerators and other residual compounds for supplementary mixing. The two-stage mixing can be carried out on the mixer or the open mill. Slow mixers or kneaders are usually used for two-stage mixing to add vulcanizing agents and accelerators at lower temperatures and have high production efficiency. The two-stage mixing time in the mixer is generally 2-4min.

Two-stage mixing can always make fine particles of carbon black better dispersion, for some compounds containing a large amount of this carbon black, no matter what type of mixer used, may have to be divided into two or more times to add as well.

Advantages of two-stage mixing: better wettability and dispersibility are required, such as extruded sealing strip compound; Compounds containing rapid vulcanizing agents or blowing agents. If the temperature in the mixer at the end of the mixing is very high, the two-stage mixing method can be used, that is, the rubber material mixed in one section is cooled down and parked, and then put into the mixer again for the second stage of mixing with vulcanizing agent. For some low-viscosity soft rubber, due to the increase of temperature in the later stage of mixing, the viscosity of the rubber becomes lower, and the shear force generated during mixing is too small to open carbon black aggregates or some agglomerated compound particles, which is the use of two-stage mixing, which can improve the dispersion of these low-viscosity soft rubbers.

The two-stage mixing method has a good effect on improving the quality of rubber materials and improving the process performance of rubber materials. It can significantly improve the dispersion uniformity of rubber and the physical and mechanical properties of vulcanized rubber; Reduces the tendency to scorch caused by sustained high temperatures.